<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        .wrap {
            width: 300px;
            margin: 100px auto 0;
        }

        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
            width: 300px;
        }

        th,
        td {
            border: 1px solid #d0d0d0;
            color: #404060;
            padding: 10px;
        }

        th {
            background-color: #09c;
            font: bold 16px "微软雅黑";
            color: #fff;
        }

        td {
            font: 14px "微软雅黑";
        }

        tbody tr {
            background-color: #f0f0f0;
        }

        tbody tr:hover {
            cursor: pointer;
            background-color: #fafafa;
        }
    </style>
</head>

<body>
    <div class="wrap">
        <table>
            <thead>
                <tr>
                    <th>
                        <input type="checkbox" id="j_cbAll" />
                    </th>
                    <th>商品</th>
                    <th>价钱</th>
                </tr>
            </thead>
            <tbody id="j_tb">
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPhone8(南京)</td>
                    <td>8000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPad Pro(北京)</td>
                    <td>5000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPad Air(东京)</td>
                    <td>2000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>Apple Watch(纽约)</td>
                    <td>2000</td>
                </tr>
            </tbody>
        </table>
    </div>
    <script>
        /* 
           需求: 
                 1. 全选，全不选。复选框，跟随全选状态变化。
                 2. 复选框点击的时候，如果全部选中，则全选选中。
        */
        //    全选按钮
        let j_cbAll = document.querySelector('#j_cbAll');
        let inputs = document.querySelector('#j_tb').querySelectorAll('input');

        j_cbAll.onclick = function () {
            this.checked;
            for (let i = 0; i < inputs.length; i++) {
                inputs[i].checked = this.checked;
            }
        }

      /*   for (let i = 0; i < inputs.length; i++) {
            inputs[i].onclick = function () {
                let sum = 0;
                for (let j = 0; j < inputs.length; j++) {
                    if (inputs[j].checked) {
                        sum++;
                    }
                }
                if (sum == inputs.length) {
                    j_cbAll.checked = true;
                } else {
                    j_cbAll.checked = false;
                }
            }

        } */

        for (let i = 0; i < inputs.length; i++) {
            inputs[i].onclick = () => {
                let flag = true;
                for (let j = 0; j < inputs.length; j++) {
                    let status = inputs[j].checked;
                    if (status) {

                    } else {
                        flag = false;
                        break;
                    }
                }
                j_cbAll.checked=flag;
            }
        }
        /* for (let i = 0; i < inputs.length; i++) {
            inputs[i].onclick = function () {
                // 标志位
                let flag = true;
                for (let j = 0; j < inputs.length; j++) {
                    // 复选框的选中状态
                    let status = inputs[j].checked;
                    if (status) {

                    } else {
                        flag = false;
                        break;
                    }
                }

                // 全选赋值
                j_cbAll.checked = flag;
            }
        } */
    </script>

</body>

</html>